Paging success rate control mechanism

ABSTRACT

A method for handling registration requests in a cellular wireless communication system. The method includes determining that a transmission-success rate of messages sent via the forward-link of an air interface is less than a threshold success rate. The method further includes, in response to the determination that the system has less than a threshold transmission success rate, increasing a frequency at which mobile stations register with the cellular wireless communication system via the air interface.

BACKGROUND

In a cellular wireless communication system, an area is divided intocells, which are further divided into cell sectors (“sectors”). Eachcell and cell sector is defined by a radiation pattern from a respectivebase transceiver station (BTS), which includes a radio-frequency antennatower. Each BTS is then typically connected with a base stationcontroller (BSC), which, together with the BTS, defines a “basestation.” Further, the BSC may then be connected with a switch (e.g.,mobile switching center (MSC)) or gateway (e.g., packet data servingnode (PDSN)) that provides connectivity with a transport network, suchas the public switched telephone network (PSTN) or the Internet. Withthis arrangement, a cell phone or other wireless communication device(generally “mobile station”) that is positioned within the coverage areaof a given sector can communicate over an air interface with the BTS andin turn via the BSC and switch or gateway with entities on the transportnetwork.

Unlike landline telephones that exist at known, fixed locations, mobilestations can operate at virtually any location where a wireless carrierprovides radio-frequency coverage. Consequently, in order for a mobilestation to be able to engage in useful communications (voice or data) ina cellular wireless communication system, the mobile station must firstregister with the system. This registration process lets the system knowwhere the mobile station is located (e.g., for purposes of directingcalls to the mobile station) and so that the system can verify that themobile station is authorized to be operating in the system.

The manner in which a mobile station registers with a cellular wirelesscommunication system can take various forms, depending on factors suchas the configuration of the system and on the communication protocolsused. For example, such registration may be accomplished using CodeDivision Multiple Access (“CDMA”). CDMA is described in further detailin Telecommunications Industry Association (“TIA”) standards IS-95A andIS-95B, which are both incorporated herein by reference in theirentirety. CDMA is also described in the International TelecommunicationsUnion (“ITU”) IMT-2000 series of standards, which are all incorporatedherein by reference in their entirety. CDMA is further described in theTIA IS-2000 series of standards, which are all incorporated herein byreference in their entirety. The IS-2000 series of standards arecommonly referred to as CDMA2000.

In a system operating according to the CDMA2000 protocol, for instance,a mobile station registers by sending over the air to the base stationan “access probe,” which carries an identifier of the mobile station andperhaps other pertinent information. The mobile station sends the accessprobe in a “slotted aloha process.” In the slotted aloha process, themobile station repeatedly sends the access probe at increasingly higherpower levels until it receives an acknowledgement message from the basestation, or until it otherwise exhausts the process (e.g., the maximumtransmission power of the mobile station is reached and noacknowledgment has been received). As is described in the CMDA2000specifications, each access probe travels in a timeslot of an airinterface access channel from the mobile station to the base station,while each registration acknowledgement travels in a timeslot of an airinterface paging channel from the base station to the mobile station.

When the base station receives an access probe from a mobile station,the base station passes the access probe along to the switch (e.g., anMSC) or other entity (e.g., a PDSN), which then responsively sends aregistration notification message to the mobile station's home locationregister (HLR). The HLR then updates the mobile station's profile toindicate where the mobile station is operating (e.g., which switch isserving the mobile station) and may further carry out an authenticationprocess, and then sends a registration response, which propagates to themobile station. If the mobile station has registered with a base stationthat is not in its “home network” (e.g., operated by the wirelessprovider with which the mobile station is associated), the registrationinformation for the mobile station is stored in a visitor locationregister (VLR) in the network in which the mobile station is operating(which may be termed “roaming”), as well as in an HLR in the mobilestation's home network.

Various trigger events can cause mobile stations to register with thesystem. In a CDMA2000 system, for instance, a mobile station willgenerally register (i) whenever it enters a new zone (e.g., sectorand/or cell) in response to a distinct “reg_zone” parameter the mobilestation receives in an air interface control channel message from thebase station, (ii) on a periodic basis, with a period indicated by a“reg_period” parameter (or directive) that the mobile station receivesin an air interface control channel message from the base station, and(iii) when the mobile station receives or places a call.

In some situations, messages transmitted from the system to a mobilestation may not successfully reach the mobile station. For example, amobile station may have moved out of a particular zone (e.g. sectorand/or cell), or the mobile station may be in a location where signalsfrom the system are attenuated or subject to interference. A decrease inthe successful transmission of messages from the system to a mobilestation can negatively impact a customer's experience by causing callsto be directed to voicemail without notifying the user, delaying thereceipt of SMS notifications, causing call set up latencies, andgenerally causing suboptimal performance of features that rely onmessages being transmitted from the system to the mobile station.

In some situations, the air interface between a base station (e.g., aparticular sector associated with the base station) and mobile stationsoperating within the coverage area of the base station can becomeoverwhelmed with too much use. This can happen, for example, if too manymobile station registrations occur at once. In a CDMA2000 system, forinstance, if access probes from two or more mobile stations line up (bychance) in the same timeslot of the access channel, an “access probecollision” occurs. The result of such a collision is that none of theprobes will succeed, principally because the base station will notreceive any of the probes in a comprehensible form due to interferencebetween the multiple access probes. Thus, should such a collision occur,each mobile station would have to re-send its access probe, because itwould not receive an acknowledgement from the base station.

In many situations, access probe collisions are not very likely to occurbecause sufficient timeslots exist on the access channel fortransmitting the access probes. However, in situations where many usersare placing calls at once, the number of access probes and access probecollisions can increase dramatically due to collisions and associatedretries. For example, after a football game or in an emergencysituation, many people within a given sector of a specific cell site mayuse their mobile phones to place calls (e.g., to call 911, to callfriends and family, to check voice mail, or for other purposes).

Each time a mobile station places a call, as was noted above, the mobilestation sends an access probe. Consequently, in a situation where manypeople within a given sector place calls at once, many access probeswill be sent at once. In turn, access probe collisions then occur and,therefore, still more (retry) access probes are sent. Further, as thesecollisions and retries are occurring, other mobile stations in thesector are periodically registering with the system, according to the“reg_period” directive from the base station, which will still furtherincrease the frequency of access probe collisions. In a CDMA2000 system,the reg_period directive includes the frequency with which mobilestations periodically register with the system. Such access probecollisions may result in mobile stations being unable to place calls,receive calls, send data and/or receive data, as the mobile stations maybe unable to successfully register with the system due to the occurrenceof access probe collisions.

Overview

Systems and methods for dynamic adjustment of radio frequencyregistration periods based on transmission-success rates and loadconditions are disclosed. These systems and methods help ensure that awireless communication system pages a target mobile station at theproper location. When a mobile station moves between coverage areas,experiences interference, or receives an attenuated or degraded signalfrom the system, messages transmitted from the system may notsuccessfully reach a particular mobile station. This situation, as wasdiscussed above, is undesirable as it may result in a mobile stationbeing unable to receive a voice call, the delayed receipt ornotification of messages, and the suboptimal performance of otherfeatures that rely on messages transmitted from the system to the mobilestation.

A method that helps to increase the likelihood that a mobile station ispaged in the proper location includes (i) determining atransmission-success rate of messages sent via a forward link of an airinterface in a cellular wireless communication system is less than athreshold success rate, and (ii) responsively increasing a frequency atwhich mobile stations register with the cellular wireless communicationsystem via the air interface. It will be appreciated that thesefunctions can be carried out by a base station, such as by a BTS and/ora BSC. However, these function can be carried out by other networkelements as well, such as by an MSC, a PDSN, or any number of othercommunication system platforms.

The process of determining that a transmission-success rate of messagesent via a forward link of an air interface in a cellular wirelesscommunication can be accomplished in a number of ways. In a firstembodiment, the process includes sending one or more page messages fromthe system to one or more mobile stations via the forward link of theair interface. Upon receipt of a page message, the mobile station maysend a message acknowledging receipt of the page message back to thesystem via the reverse link of the air interface, thus indicating asuccessful transmission. The system may determine a transmission-successrate by tracking the number of page messages sent and the number ofacknowledgments received. After computing a transmission success rate,the system may compare the transmission-success rate to a predeterminedthreshold.

In a second embodiment, the method conditions increasing the frequencyat which mobile stations register with the system on a determinationthat the air interface in the cellular wireless communication system hasless than a threshold level of load. In some situations, such as whenthere are many mobile stations concentrated in a small area, increasingthe registration frequency of mobile stations can cause a significantincrease in the load on the air interface. In a CDMA2000 system,conducting high frequency periodic registrations for mobile stationswithin the coverage area of the particular sector will add to the numberof access probes communicated to the base station and can, as a result,increase the occurrence of access probe collisions. This situation, aswas discussed above, is undesirable as it may result in the mobilestations within the coverage area of the particular sector being unableto place or receive calls and/or unable to send or receive data. Thelikelihood of overloading the air interface in this manner can bereduced by conditioning the increase in registration frequency on a loadlevel of the interface.

The process of determining that the air interface has at least athreshold level of load can be accomplished in a number of ways. In oneembodiment, the process includes detecting at least a threshold level ofreverse-link air interface load (where “reverse-link” means the airinterface link from mobile stations to the base station, as comparedwith “forward-link,” which means the link from the base station to themobile stations).

More particularly, in a CDMA2000 system, the process of this firstembodiment includes determining that at least a threshold percentage ofaccess channel timeslots are occupied over a given period of time. Thisdetermination can be made by the base station. For example, the basestation may include service logic that, when executed, determines whatpercentage of the access channel timeslots contain energy that issufficient to be an access probe within a designated time period (e.g.,every 1 minute, every 5 seconds, etc.). The number of occupied timeslots should include timeslots that contain sufficient energy torepresent an access probe but do not actually contain a verifiableaccess probe (e.g., where a cyclic redundancy check establishes that thetimeslot does not contain a legitimate access probe), as such timeslotsmay exist as the result of access probe collisions. If the determinedpercentage exceeds a designated threshold, then the base stationconcludes that the air interface has at least a threshold level of load.In this situation, the base station responsively increases the periodicregistration period (e.g., via the reg_period directive) to reduce thatloading and communicates the increased period to the mobile stationsoperating in the coverage area of the respective sector.

In another embodiment, the base station tests for the presence of atleast a threshold level of forward-link load to determine air interfaceloading. This embodiment may be implemented in conjunction with or as analternative to testing for a threshold reverse-link load. For example,in a CDMA2000 system, the base station can determine if at least athreshold percentage of paging channel timeslots are occupied over agiven period of time. As noted above, access probe acknowledgementstravel in a paging channel of the forward-link, so when the pagingchannel is more occupied, there is more likelihood that access probeacknowledgements might be delayed or not sent, thereby triggeringfurther access probes and exacerbating the access probe collisionsproblem further.

These and other aspects will become apparent to those of ordinary skillin the art by reading the following detailed description, withreference, where appropriate, to the accompanying drawings. Further, itshould be understood that the embodiments noted in this overview areonly examples and not intended to limit the scope of the invention asclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are described herein withreference to the drawings, in which:

FIG. 1 is a diagram illustrating a wireless communications system inwhich the embodiments disclosed here may be implemented;

FIG. 2 is a diagram illustrating the air interface of the wirelesscommunications system of FIG. 1 in more detail;

FIG. 3 is a diagram illustrating access probe collisions in the accesschannel of the reverse-link of the air interface shown in FIG. 2;

FIG. 4 is a diagram illustrating an arrangement of neighboring coverageareas within a wireless communication system;

FIG. 5 is a flowchart illustrating a method for dynamically adjustingmobile station registration periods based on a messagetransmission-success rate;

FIG. 6 is a flowchart illustrating a method for dynamically adjustingmobile station registration periods based on a transmission-success rateand conditioned on an air interface load condition;

FIG. 7 is a flowchart illustrating a method for dynamically adjustingmobile station registration periods based on a messagetransmission-success rate and conditioned on forward-link air interfaceload conditions; and

FIG. 8 is a flowchart illustrating a method for dynamically adjustingmobile station registration periods based on a messagetransmission-success rate and conditioned on reverse-link air interfaceload conditions

DETAILED DESCRIPTION

While embodiments of systems and methods for dynamic adjustment ofregistration periods based on load conditions are discussed generally inthe context of CDMA wireless communication systems, it will beappreciated that the invention is not limited in this respect and thatembodiments of the invention may be implemented in any number of typesof wireless communication systems, such as time division multiple access(TDMA) systems, EV-DO systems, and global system for mobilecommunications (GSM) systems, for example. As in most telecommunicationand data applications, it will also be appreciated that many of theelements of the various embodiments described herein are functionalentities that may be implemented as hardware, firmware and/or software.Additionally, many of these elements may be implemented as discretecomponents or in conjunction with other components, in any suitablecombination and location.

Organization of the Disclosure

This disclosure is organized as follows. A wireless communicationssystem (including an air interface) in which the disclosed methods andsystems may be implemented is discussed generally with reference toFIG. 1. The air interface between the mobile stations and the basestation of FIG. 1 as it relates to mobile station registration isdescribed in further detail with reference to FIG. 2. Communication ofaccess probes and access probe collisions in a reverse-link accesschannel are described with reference to FIG. 3. An arrangement ofneighboring sectors in which the disclosed methods and systems may beimplemented is described with respect to FIG. 4. And methods fordynamically adjusting the registration period for mobile stations in thesystem 100 of FIG. 1 are described with reference to FIGS. 5-8.

Wireless Communications System

FIG. 1 is a diagram that illustrates a wireless communication system 100in which the embodiments described in this disclosure may beimplemented. System 100 includes a plurality of mobile stations 105, 110and 115, which may be cellular phones, wireless personal digitalassistants, a wireless enabled computer or any other device capable ofwireless communication in system 100. System 100 generally illustrates aconfiguration of a CDMA2000 compliant system. As is indicated by thedotted line in FIG. 1, system 100 may include any number of mobilestations.

The mobile stations 105, 110 and 115 communicate, via a radio airinterface 107, with a base station 120. The base station 120 includes abase-station transceiver (BTS) 122 and a base-station controller (BSC)124. The BTS 122 communicates with the mobile stations 105, 110 and 115using radio-frequency signals over the air interface 107. The BTS 122also communicates with the BSC 124 to communicate voice and/or datainformation to and from the mobile stations 105, 110 and 115.

The base station 120 is, in turn, coupled with a switch/gateway 125. Theswitch/gateway 125 may take the form of any number of devices. Forexample, for voice communication, the switch/gateway 125 may comprise amobile switching center (MSC). Alternatively, for data communication theswitch/gateway 125 may comprise a packet data serving node (PDSN). MSCsand PDSNs are both described in further detail in the CDMA2000specifications and are not discussed in detail here for the purpose ofbrevity. Also, it will be appreciated that additional switch/gatewaydevices or systems may be coupled with the base station 120.

The switch/gateway device 125 is also coupled with a transport network130. As was described above, for voice communications, the transportnetwork 130 may take the form of the public switched telephone network.Alternatively, for data communication, the transport network 130 maytake the form of the public Internet or any suitable data network, suchas a private packet data network.

The switch/gateway 125 is further coupled with a signal transfer point(STP) 135. The STP 135 provides for the transfer of signals betweendifferent entities in the system 100. For the particular embodimentshown in FIG. 1, the STP 135 provides for transferring signals betweenthe switch/gateway 125 and a home location register (HLR) 140. Inaccordance with the CDMA2000 specification, the HLR includesregistration information for the mobile stations 105, 110 and 115. Thisregistration information includes, for example, a unique mobileidentification number for each of the mobile stations.

For any mobile station that may be operating outside its home network(e.g., “roaming”), system 100 may include the registration informationfor that mobile station in a visitor location record (VLR), which may beimplemented in conjunction with the HLR 140 or may be implementedseparately. In this situation, the registration information for theroaming mobile station is also included in an HLR of the roaming mobilestation's home network so that calls to the mobile station are properlyrouted. Additionally, the system 100 may include other entities that arecoupled with the STP 135, such as additional switch/gateways devices,service nodes, or any number of other platforms or devices for providingcommunication services in system 100.

Air Interface and Mobile Registration

FIG. 2 is a diagram that illustrates a portion of system 100, with theair interface illustrated in more detail. The elements of the system 100that are shown in FIG. 2 are those elements that are involved in theregistration of the mobile station 105 for this particular embodiment.As was discussed above, there are various trigger events that can causemobile stations to register in a CDMA2000 system. These events include(i) the mobile station 105 receiving a “reg_zone” directive from thebase station 120 via a control channel message in the air interface 107.(ii) the mobile station 105 registering on a periodic basis, with aperiod indicated by a “reg_period” directive that the mobile station 105receives in a control channel message from the base station 120, and(iii) when the mobile station 105 receives or places a call. The controlchannel is not specifically shown in FIG. 2.

The mobile station 105 registers with system 100 by sending an accessprobe via the reverse-link access channel 209 of the air interface 107.The access probe includes information that identifies the mobile station105. This information may include an indication of the service providerwith which the mobile station 105 is associated and a unique mobileidentification number of the mobile station 105. The base station 120receives the access probe and communicates the access probe to theswitch/gateway, which then responsively sends a registrationnotification message to the HLR 140 via the STP 135.

The HLR 140 then updates the mobile station's 105 profile to indicatewhere the mobile station 105 is operating (e.g., which switch/gatewayand base station are serving the mobile station 105). Additionally, theHLR 140 may also carry out an authentication process to ensure themobile station 105 is authorized to operate in the wirelesscommunications system 100. The HLR 140 then sends a registrationresponse, which propagates to the mobile station 105 via the STP 135,the switch/gateway 125 and the base station 120. The base station 120communicates the registration response message to the mobile device 105via a forward-link—paging channel 208 of the air interface 107.Regardless of the trigger that results in registration occurring, thisregistration process will be essentially the same for a mobile stationregistering in its home network.

However, as noted above, this process may be somewhat different if themobile station 105 has registered through a base station that is not inits “home network.” In this instance, the registration information forthe mobile station 105 is stored in a visitor location register (VLR) inthe network in which the mobile station 105 is operating (a “foreignnetwork”), as well as in an HLR in the mobile station's 105 homenetwork. In this situation, the mobile station 105 may be referred to as“roaming” (e.g., operating in a radio frequency coverage area outsideits home network).

Access Channel Timeslots and Access Probe Collisions

Referring to FIG. 3, a table is shown that illustrates how access probesare communicated from a mobile station to a base station. The table inFIG. 3 shows seven consecutive timeslots in the reverse-link—accesschannel 208 of the air interface 107 of FIGS. 1 and 2. The table in FIG.3 represents the timeslots of the access channel 208 for a particularsector in a wireless communications system. These timeslots aredesignated Time Slot-1 through Time Slot-7. In each timeslot, accessprobes that are communicated by the mobile stations operating in thisparticular sector are shown in respective columns. As shown in FIG. 3,ten access probes are represented, which are designated AP1 throughAP10.

For the particular situation illustrated in FIG. 3, access probecollisions would occur in timeslots Time Slot-1, Time Slot-3 and TimeSlot-5. In comparison, no collisions would occur and valid access probeswould be received (and the associated mobile devices registered) for thetimeslots Time Slot-2, Time Slot-4 and Time Slot-7. As is also shown inFIG. 3, there are no access probes present in Time Slot-6. Therefore, anaccess probe collision or mobile station registration will not occur asa result of Time Slot-6.

Because the access probes AP1, AP2 AP4, AP5, AP6, AP8 and AP9 aresubject to access probes collisions in their respective time slots,these access probes would be resent to the base station as result of thecorresponding mobile stations not receiving a registration response tothe access probes (e.g. registration will be retried). If there are alarge number of mobile devices attempting to register in the particularsector (e.g., in response to a reg_zone directive, periodicallyregistering in accordance with the reg_period directive, or registeringas part of the process of placing or receiving a call), the number oftime slots that experience access probe collisions may increase and,consequently the number of retries being attempted and associated accessprobe collisions will continue to grow.

Example Illustration of Neighboring Sectors

FIG. 4 illustrates an example arrangement of neighboring wirelesscoverage areas that may be present in a wireless communication system.As used herein, the term “wireless coverage area” may refer to eithercells or sectors within a wireless communication system. In thisexample, coverage areas 410-416 and 420-425 each contain a base stationsimilar to base station 120 depicted in FIG. 1 that can communicatewirelessly with mobile stations located within the geographic areadefined by wireless coverage areas 410-416 and 420-425.

Those skilled in the art will recognize that wireless coverage areas410-416 and 420-425 are shown in a idealized manner. In practice, thegeographic extent of wireless coverage areas 410-416 and 420-425 may bevery different than shown in FIG. 4. For example, while distinct bordersare shown between wireless coverage areas, the wireless coverage areaswill be overlapping, such that there may be many locations where amobile station can communicate with base stations in more than onewireless coverage area. As such, wireless coverage areas 410-416 and420-425 are more representative of areas of optimal wirelesscommunication.

As a mobile station moves from one wireless coverage area to another, ahandoff process may be performed to allow a mobile station to continuewireless communication while moving between wireless coverage areas.Typically, a switch such as switch 125 depicted in FIG. 1 is responsiblefor switching calls to the base stations located within wirelesscoverage areas 410-416 and 420-425, and also controls handoffs betweenbase stations within wireless coverage areas.

To facilitate handoffs between base stations within wireless coverageareas, a neighbor list is associated with each wireless coverage area410-416 and 420-425. The neighbor list identifies other wirelesscoverage areas that are good candidates for receiving handoffs from agiven wireless coverage area. For example, the neighbor list forwireless coverage area 410 may include wireless coverage areas 411-416and 420-425. The neighbor list may also be arranged to reflect apriority order based on proximity of the wireless coverage areas, signalstrength, or other parameters. For example, the neighbor list associatedwith wireless coverage area 410 may designate wireless coverage areas411-416 as first-tier neighbors based on their proximity to wirelesscoverage area 410, and prioritize wireless coverage areas 411-416 asgood candidates for handoffs.

The neighbor lists associate with each wireless coverage area 410-416and 420-425 are typically stored in a database accessible by the switchresponsible for controlling handoffs. Also, in a CDMA system, neighborlists are also transmitted to mobile stations, which may allow mobilestations to monitor control information sent from a number of differentwireless coverage areas. Various techniques for adjusting theregistration frequency will now be described with reference to FIGS.5-9.

Methods for Dynamically Adjusting a Mobile Station Registration Period

FIGS. 5-8 are flowcharts that illustrate various methods for dynamicallyadjusting a periodic registration period for mobile stations operatingin a particular sector of a wireless communications system. The methodsillustrated in FIGS. 5-8 are discussed with reference to FIGS. 1-4.Again, while these methods are described generally in the context of aCDMA2000 wireless communications system, other implementations arepossible, such as in a GSM wireless communication system, or in an EV-DOsystem for example.

FIG. 5 is a flow chart that illustrates a high level method 500 fordynamically adjusting the radio-frequency registration period for mobilestations operating in a wireless communications system, such as theregistration period associated with the reg_period directive in a CDMA2000 wireless communications system. The method 500 includes, at block510, determining that the transmission-success rate is less than athreshold level. As used herein, “transmission-success rate” refers to asuccess rate of messages sent via a forward link of an air interface ina cellular wireless communication system. In one implementation of themethod, the messages sent via the forward link of the air interface arepage messages sent from the wireless communication system to one or moremobile stations. When a page message is received by the mobile station,the mobile station sends an indication acknowledging receipt of the pagemessage back to the wireless communication system via the reverse linkof the air interface.

The wireless communication system can calculate the transmission-successrate by comparing the number of messages sent to mobile stations via theforward link of the air interface to the number indications the wirelesscommunication system receives back from the mobile stations. Thewireless communication system can then compare the calculatedtransmission-success rate to a predetermined threshold and determinewhether the transmission-success rate is less than the threshold successrate.

The calculation of the transmission-success rate can be done on a numberof different scales within the wireless communication system. Forexample, the transmission-success rate can be performed on asector-by-sector basis, for the entire wireless communication system, orfor subsets of a plurality of sectors within the wireless communicationsystem.

If the wireless communication system determines that the transmissionsuccess rate is less than the threshold success rate, the wirelesscommunication system can responsively increase the frequency with whichmobile stations are required to register with the system, as shown inFIG. 5 at block 520. As indicated in FIG. 5, block 530, the wirelesscommunication system can then transmit this increased registrationfrequency to the mobile stations. In a CDMA system, this can be achievedby decreasing the registration period in the reg_period directive sentto mobile stations.

The process of changing the registration period parameter could beimplemented using service logic that is stored and executed on the BSC124, for example. Of course, such service logic could be stored andexecuted elsewhere in the system 100, such as in the switch/gateway 125,as one alternative. Once the registration period parameter is decreased,the new value of the parameter is communicated to the mobile stations105, 110 and 115 in the reg_period directive, which is communicated inthe control channel of the forward-link of the air interface 107.

After receiving the revised registration period parameter, the mobilestations 105, 110 and 115 adjust the period at which they periodicallyre-register with in the system 100 in accordance with the modifiedregistration period. This results in an increase in the number ofperiodic registrations in a given time period and corresponding decreasein the likelihood of a missed page message.

The increase in registration frequency may also be implemented on avariety of scales within the wireless communication system. For example,if a first sector is identified as having a transmission-success ratebelow the threshold success rate, the registration frequency can beincreased in the first sector, as well as in the other sectors near thefirst sector. Such sectors can be identified and selected by thewireless communication system by using the neighbor list of the sectorwith the low transmission-success rate. In some implementations of themethod, the registration frequency is increased in the sectors that arefirst-tier neighbors of the sector with the low transmission-successrate. In other implementations of the method other portions of theneighbor list, or even the entire neighbor list, may be used to identifysectors that should increase their required registration frequency. Byincreasing the registration frequency in sectors with lowtransmission-success rates and their neighboring sectors, mobilestations that are moving between adjacent sectors are required toregister with the system more frequently, thus increasing the likelihoodthat the mobile station will be paged in the correct location.

As shown in FIG. 6, at block 620, the increase in registration frequencymay be conditioned on a determination that the air interface has lessthan a threshold level of load. Since increasing the frequency at whichmobile stations register with system increases the number of mobilestations attempting to communicate with the system via the air interfaceat any one time, it is possible that an increase in the registrationfrequency could overload a portion of the wireless communication systemand cause undesired disruptions in service.

The determination that there is less than a threshold level of load onthe air interface can be made in a number of ways. For example, such adetermination may be made by determining that a certain percentage ofbandwidth of the air interface (or of a certain channel of the airinterface) is occupied communicating wireless signals between the mobilestations 105, 110 and 115 and the base station 120.

Once it is determined that the air interface 107 has at least thethreshold level of load, the frequency of registration is increased andtransmitted to the mobile stations, as depicted in blocks 630 and 640,respectively.

FIG. 7 is a flowchart that illustrates a method 700 for adjusting theperiodic registration period based on the transmission-success rate ofmessages sent via the forward link of the air interface and conditioningthe registration period adjustment on the forward-link load of the airinterface for mobile stations operating in system 100. The method 700includes, at block 710, determining that the transmission-success rateof messages sent via the forward link of the air interface is less thana threshold success rate. The method also includes, at block 720,determining that the forward-link has at least a threshold level ofload. As indicated in block 720, this determination can be made bydetermining the number of timeslots in the forward-link paging channel208 of the air interface 107 that are occupied. For the method 700, theoverall occupancy of the paging channel 208 may be determined (e.g.,regardless of the type of information being communicated in each of thepaging channel 208's timeslots) or, alternatively, the occupancy of thepaging channel's 208 timeslots may be determined based on the number oftimeslots that are carrying access probe acknowledgements (responses toregistrations requests).

In operation, the base station 120 will know how many access probeacknowledgements (or other types of paging channel messages) it issending on the forward-link paging channel 208 in a given period oftime, as well as how many timeslots are available on the forward-linkpaging channel 208 in the given period of time. The base station 120 maymonitor the number of access probe acknowledgments using service logicthat is present and executed on the BSC 124, for example. Then, based onthis information, the base station 120 can readily determine whatpercentage of the forward-link paging channel's 208 timeslots areoccupied with access probe acknowledgments (or with other types ofpaging channel messages). Based on this percentage, the base station 120can determine if the load is under the threshold before permitting anadjustment to the periodic registration period.

Alternatively, the base station 120 could perform the forward-linkthreshold analysis by comparing the number of access probeacknowledgements that are scheduled to be sent in a given period of timewith the number of acknowledgements that it is actually able to send inthat period of time to determine an occupancy percentage for theforward-link paging channel 208. The base station 120 may then comparethis percentage to the designated threshold to determine if anadjustment to the periodic registration period is appropriate.

As with the methods 500 and 600, the process of changing the periodicregistration parameter based on the loading of the forward-link of theair interface 107 may be accomplished using service logic that isimplemented in, for example, the BSC 124 of FIG. 1. For the method 700,the base station 120 communicates the modified registration periodparameter to the mobile stations 105, 110 and 115 in a control channelmessage (e.g., the reg_period directive) over the air interface 107 atblock 730. After the modified parameter is received by the mobilestations, they will conduct their periodic registrations in accordancewith the new registration period.

FIG. 8 is a flowchart that illustrates a method 800 for adjusting theperiodic registration period based on the transmission-success rate ofmessages sent via the forward link of the air interface and conditioningthe registration period adjustment on the reverse-link load of the airinterface for mobile stations operating in a wireless communicationssystem, such as system 100 of FIG. 1. The method 800 includes, at block810, determining that the transmission-success rate of messages sent viathe forward link of the air interface is less than a threshold successrate. The method 800 also includes, at block 820, determining that thereverse link has at least a threshold level of load. As indicated inblock 820, this determination can be made by determining the number oftimeslots in an access channel of the reverse-link of the air interface107 that contain sufficient energy to represent an access probe.

Referring to the table in FIG. 3, for this situation, this determinationwould result in all of the timeslots except Time Slot-6 being determinedto include sufficient energy to represent an access probe. Therefore,approximately 85% of the timeslots would be determined as being“occupied.” However, Time Slot-1, Time Slot-3 and Time-Slot 5 would nothave a verifiable access probe (e.g., verified using a CRC) due to theaccess probe collisions that would occur in those time slots.Nevertheless, the fact that an access probe collision occurs in each ofthese slots makes it desirable to designate those slots as occupied sothat they are accounted for in determining the load on the reverse linkaccess channel 209 of the air interface 107. This determination can bemade, for example, using service logic that is implemented in the basestation 120 that monitors the number of occupied timeslots on the accesschannel 209 over a particular time period and determines the percentageof occupancy based on the number of timeslots available during thatparticular time period.

If the threshold for reverse-link load in the method of FIG. 8 were setat 90%, the situation illustrated in FIG. 3 would permit a decrease inthe periodic registration period, because the 85% occupancy for thesituation illustrated in FIG. 3 is less than a threshold of 90%. Once itis determined that there is less than the threshold level of load(occupancy) on the reverse-link—access channel 209 of the air interface107 (e.g., less than 90%), the periodic registration frequency for themobile stations is increased at block 830. As such, the increase in theperiodic registration frequency is made in response to the determinationthat the transmission-success rate of messages sent on the forward linkis less than a threshold level and conditioned on a determination thatthe level of load on the air interface is below a threshold level.

The increase in frequency depends on the particular situation and may bedynamically adjustable based the number of adjustments that have beenmade in a certain period of time, or the increase may be predetermined.The process of changing the periodic registration period parameter mayalso be accomplished using service logic that is implemented in, forexample, the BSC 124 of FIG. 1. At block 840, the base station 120communicates the modified registration period parameter to the mobilestations 105, 110 and 115 in a control channel message (e.g., reg_perioddirective) over the air interface 107. Once the modified registrationperiod parameter is received, the mobile stations 105, 110 and 115 willconduct their periodic registrations in accordance with the modifiedparameter.

After the registration period parameter is modified, the base station120 may continue to monitor the transmission-success rate and the loadon the air interface 107 (in this case, the reverse-link). If thetransmission-success rate increases above the designated threshold, thebase station 120 may increase the registration period to its originalvalue. For example, the increase of the registration period to itoriginal value may be done incrementally in response to severaldeterminations that the transmission-success rate is above thethreshold. If the load increases above the designated threshold (e.g.,90% in the above example) the base station 120 may restore theregistration period parameter to its original value and communicateanother reg_period directive to the mobile stations, which will thenresume periodic registration at the original (e.g., default)registration period after receiving this directive.

The methods 700 and 800 of FIGS. 7 and 8 may be implemented individuallyor may be implemented together. For example, implementing methods 700and 800 together may permit multiple conditions to be placed on anincrease in the registration frequency made in response to adetermination that the transmission-success rate of messages sent viathe forward link of an air interface is below a threshold level. In anembodiment where the methods 700 and 800 are implemented together, thebase station 120 would detect that the transmission-success rate ofmessages sent via the forward-link of the air interface was less than athreshold success rate.

Before increasing the registration frequency in response to thesub-threshold transmission-success rate, the base station 120 would alsoconfirm that the forward-link load (e.g., paging channel 208 occupancy)was less than a first designated threshold and that the reverse-linkload (e.g., access channel 209 occupancy) was less than a seconddesignated threshold. Based on the determinations that the forward-linkload and the reverse-link load are both under their designatedthresholds, the base station 120 will permit that a responsive increasethe periodic registration frequency, such as in the manner describedabove.

CONCLUSION

Various arrangements and embodiments in accordance with the presentinvention have been described herein. It will be appreciated, however,that those skilled in the art will understand that changes andmodifications may be made to these arrangements and embodiments, as wellas combinations of the various embodiments without departing from thetrue scope and spirit of the present invention, which is defined by thefollowing claims.

1. A method for handling registration requests in a cellular wirelesscommunication system, the method comprising: the cellular wirelesscommunication system making a first determination that atransmission-success rate of messages sent via a forward link of an airinterface in the cellular wireless communication system is less than athreshold success rate; the cellular wireless communication systemmaking a second determination that the air interface has less than athreshold level of load, at least in part by determining (i) that accesschannel time slot occupancy percentage on a reverse link of the airinterface is lower than a threshold access channel time slot occupancypercentage and (ii) that paging channel time slot occupancy percentageon the forward link of the air interface is lower than a thresholdpaging channel time slot occupancy percentage; and responsive to thefirst determination and second determination, the cellular wirelesscommunication system increasing a frequency at which mobile stationsregister with the cellular wireless communication system via the airinterface, wherein increasing the frequency at which mobile stationsregister with the cellular wireless communication system via the airinterface comprises decreasing a registration period in aregistration-period directive to the mobile stations.
 2. The method ofclaim 1 wherein the messages sent via the air interface are pagemessages.
 3. The method of claim 1, wherein determining that the accesschannel time slot occupancy percentage is lower than a threshold accesschannel time slot occupancy percentage comprises detecting that there isless than a threshold percentage of access channel timeslots containingenergy sufficient to represent an access probe.
 4. The method of claim1, further comprising operating a base station in the cellular wirelesscommunication system to carry out the determining and increasing steps,wherein the mobile stations are within a coverage area of the basestation.
 5. The method of claim 1, whereby the mobile stations respondto the registration-period directive by attempting to register with thecellular wireless communications system via the air interface at theincreased frequency.
 6. The method of claim 5 further comprising:identifying a first sector of the cellular wireless communication systemwherein there is less than the threshold success rate; and sending theregistration-period directive, including the decreased registrationperiod, in a set of sectors of the cellular wireless communicationsystem.
 7. The method of claim 6, wherein the set of sectors is definedby a neighbor list.
 8. The method of claim 7, wherein the neighbor listis arranged in a predetermined priority order, and the set of sectorscomprises a set of first-tier neighbors of the first sector.
 9. Themethod of claim 8 wherein the set of sectors comprises all of thefirst-tier neighbors of the first sector.
 10. A base station for use ina cellular wireless communications system, the base station includingstored service logic that, when executed, provides for: making a firstdetermination that a success rate of messages sent via an air interfacein the cellular wireless communication system is less than a thresholdsuccess rate; making a second determination that an air interface in acellular wireless communication system has less than a threshold levelof load, at least in part by determining (i) that access channel timeslot occupancy percentage on a reverse link of the air interface islower than a threshold access channel time slot occupancy percentage and(ii) that paging channel time slot occupancy percentage on the forwardlink of the air interface is lower than a threshold paging channel timeslot occupancy percentage; and responsive to the first determinationthat the success rate of messages sent via the air interface is lessthan a threshold success rate and the second determination that the airinterface has less than a threshold level of load, increasing afrequency at which mobile stations register with the cellular wirelesscommunication system via the air interface, wherein increasing thefrequency at which mobile stations register with the cellular wirelesscommunication system via the air interface comprises decreasing aregistration period in a registration-period directive to the mobilestations.
 11. A method for handling registration requests in a cellularwireless communication system, the method comprising: the cellularwireless communication system making a first determination that atransmission-success rate of messages sent via a forward link of an airinterface in the cellular wireless communication system is less than athreshold success rate; the cellular wireless communication systemmaking a second determination that the air interface has less than athreshold level of load, at least in part by (i) comparing a number ofaccess probe acknowledgements that are scheduled to be sent in a periodof time with forward link paging channel capacity in the period of timeto determine a paging channel occupancy percentage, and determining thatthe paging channel occupancy percentage is lower than a threshold pagingchannel occupancy percentage, and (ii) determining, based on energylevel in reverse link access channel timeslots, that access channel timeslot occupancy is lower than a threshold access channel timeslotoccupancy percentage; and responsive to the first determination andsecond determination, the cellular wireless communication systemincreasing a frequency at which mobile stations register with thecellular wireless communication system via the air interface, whereinincreasing the frequency at which mobile stations register with thecellular wireless communication system via the air interface comprisesdecreasing a registration period in a registration-period directive tothe mobile stations.